1. Field of the Invention
2. Description of the Prior Art
One power semiconductor module of the type with which this invention is concerned has been disclosed in International Patent Application WO 98/15005, for instance, and has a plurality of semiconductor components which are electrically connected on the top side to a conductor track plane of a first carrier substrate and on the bottom side to a conductor track plane of a second carrier substrate. The stack formed of the two carrier substrates and the semiconductor components disposed between them can be enlarged by stacking further carrier substrates one above the other, with one layer of semiconductor components provided between each two carrier substrates. To improve the heat dissipation, a metal plate that acts as a heat sink is disposed on at least one of the two outer carrier substrates.
To protect the electronic circuit from moisture and dirt, the arrangement comprising the stack and the heat sink must be inserted into a hermetically sealed housing part. A disadvantage of this is that the heat first flows away to the heat sink and only then can it reach the outside through a housing wall. If the heat sink is at the same time a housing wall, for instance in the form of a metal housing bottom, then hermetically sealing off the housing presents major problems. Since the heat sink must be quiet large to achieve efficient cooling, an overall inconveniently large structure has to be hermetically encapsulated, and the design of the housing depends on the size of the heat sink or cooling body used. The heat sink in the encapsulated housing can no longer be altered afterward, so that flexible adaptation of the cooling body to the type and number of heat-generating semiconductor components is impossible.
A further difficulty is that because of the major heat production of power semiconductors, the power semiconductor module must in many cases be cooled with a coolant fluid. In the known arrangements, cooling conduits through which a coolant fluid flows must be made in a complicated way in the cooling body. Since the cooling conduits are embodied on the cooling body located in the housing interior, considerable effort is required to enable delivering the coolant into the hermetically sealed housing and removing it again.
The foregoing and other disadvantages are overcome in the power semiconductor module of the invention in which the topmost and bottommost carrier substrate of the stack at the same time forms an upper and lower housing wall of the power semiconductor module, respectively, and the heat generated by the semiconductor components is dissipated to the outer carrier substrates, it is attained that the heat from the outer carrier substrates can be radiated directly to the exterior surrounding the housing part and is not dissipated inside the housing part to a cooling body. The housing part advantageously includes not only the upper and lower housing walls formed of the outer carrier substrates but also an encompassing wall forming the four side walls of the housing part, the encompassing wall being secured to the carrier substrates. It is thus simple to achieve a hermetically sealed and extremely compact design that furthermore enables very efficient heat dissipation to the surroundings of the housing. It is especially advantageous that without any complicated shaping of cooling conduits and without modifying the housing structure, the power semiconductor module of the invention can be inserted into a bathing coolant medium or can be contacted to a cooling body. Advantageously, the heat dissipated to the outer carrier substrates is radiated directly to the respective preferred heat sink. Because of the manifold, flexible usage possibilities, the power semiconductor module of the invention offers considerable advantages over the versions known from the prior art.
Because the electrically contacting of the semiconductor components to the respective carrier substrate disposed above the semiconductor component and to respective carrier substrates disposed below the semiconductor component is brought about by soldering, especially rapid dissipation of the heat in the stack to the outer carrier substrates is made possible.
The heat dissipation can be improved still further in that the interstices between the stacked carrier substrates are completely filled by a flowable, curable and heat-conducting medium.
Advantageously, the flowable, curable and heat-conducting medium can be applied simultaneously to the carrier substrate face ends, extending perpendicular to the main surfaces of the carrier substrates, in such a way that the flowable, curable medium forms the encompassing wall. This obviates one additional production step for fixation of the wall to the stack.
Advantageously, as the flowable, curable and heat-conducting medium, a capillary flowable adhesive can be used.
In another exemplary embodiment, it is provided that the flowable, curable and heat-conducting medium comprises an injection molding composition. The stack comprising the carrier substrates and the semiconductor components can then be produced for instance by an injection molding process, or by transfer molding.
Advantageously, the terminals of the power semiconductor module are formed by contact elements, which are each electrically contacted to a respective conductor track disposed on a carrier substrate and are extended laterally out of the interstices between the carrier substrates and are extended through the encompassing wall to the outside out of the housing part. If the encompassing wall comprises an electrically conductive material, then insulating leadthroughs for the contact elements can for instance be provided. To achieve a hermetically sealed closure of the housing part, the insulating leadthroughs, for instance in the form of glass leadthroughs, can each be introduced into a respective recess of the encompassing wall.
In another exemplary embodiment, it is provided that the encompassing wall is affixed at least in part to the carrier substrate face ends that extend perpendicular to the main surface of the carrier substrates. For instance, the wall can be produced from a single metal strip, which is glued or soldered or affixed in some other way to the face ends of the carrier substrates.
It is especially advantageous to embody the encompassing wall by means of at least one closed encompassing frame, which is placed between an upper and a lower carrier substrate in such a way that at least the at least one semiconductor component is completely surrounded by the frame, and the frame is tightly joined to the upper carrier substrate and the lower carrier substrate. In this case, one frame is required for each interstice between two carrier substrates.
Preferably, the frames are embodied as metal frames and are soldered over a large surface area to an encompassing conductor track of the upper carrier substrate and to an encompassing conductor track of the lower carrier substrate. The soldering of the frames is advantageously done together with the soldering of the semiconductor components to the conductor tracks of the carrier substrates. The production of a power semiconductor module of this kind can be performed especially simply and reliably. Since the encompassing frames do not allow the terminals to be extended to the outside laterally from the interstice between the carrier substrates, the electrical terminals of the semiconductor components are extended to the outside via via-holes in the carrier substrates and on the outside of the outer carrier substrates are electrically connected to contact elements.
In another advantageous exemplary embodiment of the invention, it is provided that in the stack, at least one carrier substrate is disposed with an elastically resilient layer, and the stack formed is elastically resiliently compressible in a direction perpendicular to the plane of the carrier substrates. This advantageously makes it possible for the power semiconductor module to be inserted into a suitably designed groove or pocket in a cooling body, and by the clamping force of the elastically resilient layer, the outer carrier substrates are pressed firmly against the cooling body. A screw connection is not needed for this purpose. The elastically resilient layer can for instance be fabricated from an elastically deformable plastic. In another exemplary embodiment, it is provided that the elastically resilient layer be embodied by a plurality of spring elements disposed in the same plane.